This invention relates to techniques for obtaining radiographic images and, more particularly, to a method and apparatus for obtaining improved radiographic images of opacified anatomy, including information concerning blood flow rate, using a fluoroscopic type of equipment in conjunction with a video processor.
A typical X-ray fluoroscopy apparatus includes an X-ray source and an image intensifier which is used to detect the X-radiation. The output of the image intensifier is viewed by a television camera, and the resultant television signal can be presented on a monitor and/or recorded. When a body, such as that of a patient, is interposed between the X-ray source and the detector, X-rays are absorbed in varying degrees depending upon the thickness and composition of different regions of the body. This results in the presentation of a two-dimensional image that can be used, for example, for diagnosing structural abnormalities within the body.
The ability to "see" structure in the body using the described technique depends on the X-ray absorption properties of the structure of interest in relation to the X-ray absorption properties of the material(s) adjacent to the structure. The greater the difference, the greater the "contrast" the structure of interest will have in the resulting television image. The greater the contrast, the greater the clarity of the structure in the image. Consequently, achieving high contrast is a desirable quality with this imaging procedure.
Radiographic contrast agents are used to create a large difference in X-ray absorption behavior where little or none previously existed. For example, blood vessels are virtually invisible on fluoroscopic images (except in the chest) because blood, muscle, fat and soft tissue all possess similar X-ray absorption behavior. Radiographic contrast agents contain material (e.g. air, barium, iodine) which has X-ray absorption properties dissimilar to blood, muscle, fat and the soft tissue. For example, when a bolus of iodinated liquid contrast material is injected into an artery or vein, the vascular structure is given artificially higher contrast on an X-ray image while the contrast material is present within a certain vascular segment. The contrast agent, flowing along with the blood, rapidly washes out of one segment and moves on to the next. In order to outline large segments of vasculature, large boluses of long duration (several seconds) usually are administered. Since iodinated contrast agents are toxic and present small but significant patient discomfort, as well as some risk of serious complications, only limited quantities are used in common procedures.
In the copending U.S. application Ser. No. 333,558, now U.S. Pat. No. 4,436,095 assigned to the same assignee as the present application, there is disclosed a technique which reduces the amount of contrast material needed for a given procedure, and/or enhances the image which can be obtained when using a given amount of contrast material. This is achieved by storing, at each pixel of a video image, the video signal level representative of the maximum opacification during a sequence of video frames during which the bolus passes through a blood vessel of interest. Since maximum opacification of each portion of the vessel occurs when the concentration of contrast material is greatest, the disclosed technique permits visualization of the vessel as if the contrast material was present throughout at its maximum cencentration.
It is among the objects of the present invention to generate improved processed images of the internal structure of a body, and also to obtain the travel time of blood between selected points in a vessel so that blood flow can be determined.